I have always been intrigued by tools that have provided similar functions as the Dock to other operating systems: in the classic Mac OS, there was the control strip, and I even appreciated the "quick launch" feature in Windows XP. I have enjoyed seeing new features and refinements added to the OS X Dock over the years; and in Snow Leopard, Apple has added a few new features that may be useful to some people, but which can easily be overlooked if you use the Dock in the same way as you did with Leopard.
1. Minimize into applications
The standard minimization behavior for OS X windows is to go to a unique space in the Dock; however, this can make the Dock uncharacteristically long if you use a lot of windows. In Snow Leopard, Apple has provided the option to minimize windows into the icon of their application. This allows the Dock to maintain its normal size and shape even if you have many windows minimized to it. This can be set in the Dock system preferences.
I have looked forward to something like this in the Dock for a while, however while useful it does appear that the current implementation is a bit incomplete. If you minimize several windows for an application, the way to get one back is to click the application again and one would expect that subsequent clicks would bring back the remaining windows. This is not the case, and the only way to retrieve additional hidden windows is to right-click the application icon in the Dock and select the window.
2. New shortcuts to expose
If you click and hold an open application in the Dock, you will activate Expose for the open windows of that application. This is a very convenient addition to the Dock and Snow Leopard reviewers and users seem to have welcomed it warmly.
3. Options key for more menu options
Along with quick access to Expose, if you click and hold an application you will get a small menu of options that include managing the application's position in the Dock, and hiding or quitting the application. If you press the options key with this menu open, you will see the menu options will change to "force quit" and "hide others."
4. Same old customizations
Perhaps my favorite Dock feature has been a hidden one, which is to move it to the corner of my screen instead of being in the center of it. To do this, you will have to apply some hidden preferences to the Dock, which can be easily done by issuing the following command in the Terminal:
defaults write com.apple.Dock pinning POSITION; killall Dock
In this command, change "POSITION" to either "start", "middle", or "end". These will put the Dock on the left, middle, or right side of the screen; or, if you have the Dock on the side of your screen, these options will move the Dock to the top, middle, or bottom of the screen.